Noise dosimeters are commonly used for measuring the accumulative exposure to noise, for instance over an entire work shift, in order to see if the noise exposure of a worker is within the norms of the regional or national regulations on noise exposure.
Noise is composed of many different types of noise, such impulse noise being short noise bursts having a duration of less than 1 second and continuous noise having a duration of 1 second or more. These two types of noise can also be measured as a time-weighted average (TWA), which is the average of both impulse noise and continuous noise over a given time, for instance 8 hours.
The maximum noise levels allowed for impulse noise, continuous noise and TWA at a work place is a matter of national or regional regulations. In the US for instance, the maximum impulse noise is 140 dB sound pressure level, the maximum continuous noise is 115 dBA (measured on the slow average “A” scale) and the maximum eight-hour TWA is 90 dBA.
Noise exposure is either measured via a direct method or an indirect method. In the direct method a noise dosimeter is worn by the worker during the work shift and the noise levels are evaluated in the actual environment of the worker. However, there does not exist any effective direct method of measuring the noise exposure of a worker using a headset or earphones.
In the indirect method, the headset or earphones are placed on an artificial head that measures the sound pressure applied to its ear(s). The indirect method has a number of flaws, since it does not compensate for the fact that a worker might wear the headset slightly different during a work shift and does not compensate for the individual variations in the shape of the head or ears of the worker, which may significantly impact the level of the actual sound pressure applied to the ear.
Users of communication headsets, such as people working in a call centre, are exposed to a large quantity of sound during a work shift, since sound from the headset speaker is sent directly into the ear for many hours. Therefore, it is important to obtain accurate measurements of the sound exposure levels of users wearing a headset in order to evaluate the influence of wearing a headset for many hours.